Issue 112 Item 3 Night-Light May Prevent Diabetic Eye Damage

An illuminating theory may lead to a simple way to prevent a common cause of blindness among diabetics. Researchers from the U.K. suggest that a condition known as diabetic retinopathy might be avoided by sleeping with the lights on. But they add that more studies are needed to prove that their bright idea can actually save sight.

New research supports the theory that hours of complete darkness increases retinal damage from diabetes–and that sleeping with some lights on could help counter the effect.

However, it’s too soon to recommend diabetics keep the bedroom lights on every night to cut their risk of the eye damage–known as diabetic retinopathy. For one, chronic exposure to light during sleep could have some unforeseen effects.

Diabetic retinopathy is a common complication of diabetes that can lead to blindness. It is caused by changes in retinal blood vessels.

Drasdo, of Cardiff University in Wales, explained that some researchers believe that oxygen deprivation in the retina during dark hours promotes diabetic retinopathy.

In their study, Drasdo and his colleagues looked at seven adults with Type 2 diabetes but no apparent retinopathy, and compared them with eight non-diabetics. They found that activity in tissue near the surface of the retina was reduced after being in the dark, but was bumped up with exposure to oxygen. Healthy individuals showed no such changes.

Professor Neville Drasdo and colleagues offer direct evidence that diabetic retinopathy is caused by a lack of oxygen, occurring within the inner layers of the retina during darkness. Previous research has shown that oxygen levels in the retina of diabetics fall as the eyes adapt to dark.

The researchers tested the effect of breathing in 100% oxygen — normal air is 21% oxygen — on the eyes of seven people with type 2 diabetes and eight people without diabetes. The diabetics had the disease for an average of about seven years. None of the patients had been diagnosed with retinopathy, but they all had evidence of too little oxygen within the retina during darkness.

With high oxygen treatment, the eyes of the diabetic patients returned to normal.

Drasdo stated that the findings expand on earlier research indicating a link between a lack of oxygen and diabetic retinopathy. He also suggests that it’s likely that the lack of oxygen is what is causing the increase in blood vessels in the eye — thus the retinopathy.

The researchers suggest that sleeping with the lights on could prevent retinopathy in diabetics because light through closed eyelids suppresses the eyes’ ability to adapt to the dark. Drasdo says the nighttime light therapy would have to be permanent because it takes up to two decades for retinopathy to develop in diabetics. And he adds that the long-term consequences of this preventive treatment are not known.

The findings are published in the June 29th issue of The Lancet.

However, he added, more research is needed before diabetics start taking on a permanent, "full night-time illumination" regimen.

Drasdo also noted that sticking with a diabetes management plan aimed at controlling blood sugar levels can help ward off diabetic retinopathy. SOURCE: The Lancet 2002;359:2251-2253.